Conventional orthogonal frequency division multiplexing (OFDM) receivers are designed assuming the cyclic prefix (CP) is longer than the maximum excess delay (MED) of the desired users channel, thereby reducing intersymbol interference (ISI). Users in adjacent bands are assumed to cause negligible adjacent channel interference (ACI). This is achieved by avoiding channels with maximum excess day longer than the cyclic prefix by elongating the cyclic prefix durations, such as the extended-CP option in Long Term Evolution (LTE). Possible adjacent channel interference due to interferers in adjacent bands are either mitigated using interference cancellation or avoided by increasing guard bandwidth until adjacent channel interference power becomes negligible or suppressed.
There are numerous approaches known for suppressing ACI. The most prominent approach is windowing, which is popular due to its low computational complexity and efficacy. Windowing can be applied at the transmitter to reduce out-of-band (OOB) emission and corresponding ACI before it eventuates, or alternatively, windowing can be used at the receiver to reject present ACI. However, known windowing techniques utilize the same window function for all subcarriers, while it is known that edge subcarriers are critical in out-of-band emissions and are more prone to present ACI. Subcarrier specific windowing (SSW) techniques at both the transmitter and receiver are known in the art. However, the known SSW implementations assume that the cyclic prefix (CP) is longer than the maximum excess delay (MED) of the channel, to accommodate windowing and limit the window length to the guard interval that is not disturbed by multipath reception. Implementations of subcarrier specific windowing are also known to allocate additional samples for windowing, thereby reducing spectral efficiency, which is undesirable.
Cellular communication standards beyond 5G are envisioned to simultaneously provide diverse services, with various requirements, to a myriad of devices. Increasing spectral efficiency is crucial to effectively supporting the projected number of devices, particularly in lower carrier frequencies, thereby favoring reduced guards. Using cyclic prefix durations shorter than the users' maximum excess delay have been proposed to satisfy the lower latency required by new services in systems beyond 5G, while also increasing spectral efficiency.
However, the conventional approaches do not address the requirements of communication systems beyond 5G. Asynchronous, non-orthogonal waveforms with different parameterizations, referred to as numerologies, are also proposed to be used in adjacent bands to provide diverse services in future standards. However, determining the adjacent channel interference (ACI) caused by such non-orthogonal numerologies has not been previously addressed.
Accordingly, what is needed in the art is an improved system and method that addresses the additional requirements of communication systems beyond 5G, including increased spectral efficiency and adaptations for non-orthogonal numerologies.